Make the lines pretty to look at xD
Use a little bit of shading...
I suck at shading, so don't try to shade like me ^^

Step 4

Then go to the menu on the left, click on edit, and then on copy.
Open a new layer (I only used two layers.) and paste it there. Then go to effects and select flip horizontal. This is what you should get.

Step 5

You can also go to effects, and select invert.
That was my tut, good luck ^^